One conventional way of testing semiconductor devices such as communications chips is to use a logic analyser, which is an external system that connects to certain data paths, typically via preallocated pin connections. The logic analyser can then be used to investigate whether or not the chip is performing correctly by intercepting data flows to and from the chip, and also potentially by injecting certain data into the chip. However, in doing so the analyser probes load the transmission media, and so can destroy the signals. In addition, as semiconductor devices such as communications chips incorporate higher and higher densities of components and operate at ever-rising frequencies, it is becoming increasingly difficult to use such a conventional logic analyser.